The raw syngas (raw gas) from the fluidized bed coal gasifier must go through cooling and dust removal processes before desulfurizing and decarburizing processes in the next stage in order to obtain qualified syngas (clean gas). Wet dust removal method is commonly used in the prior art, but will seriously result in secondary pollution and water treatment problems. For example, after the deposition of primary black water generated by water-washing method, secondary black water needs further biochemical treatment. Equipments and processes for the biochemical treatment of the black water from wash water are quite costly. Plate heat exchanger used in the water-washing method is also very easily blocked by wet mud, which will result in shutdown during the production, so the plate heat exchange has to be frequently disassembled and washed by chemical agents. Meanwhile, the carbon mud will contain high content of water after the deposition of the black water, and the wet carbon mud cannot be recycled in the industry and treated as three wastes. Accordingly, there is an urgent need to provide an innovative and improved dust removal technology to process the raw syngas from the fluidized bed coal gasifier.
A dust removal system using baghouse filter for blast furnace gas is disclosed in a Chinese utility model patent with Publication No. CN2828056 to remove dusts from blast furnace gas. A big dry-type dust remover using baghouse filter for blast furnace gas is also disclosed in a Chinese utility model with Publication No. CN201008774 to remove dusts from blast furnace gas. The blast furnace gas is different from the raw syngas produced by the fluidized bed coal gasifier, for example, the blast furnace gas contains no steam and far less dusts (the blast furnace gas contains about 20 g/m3 dusts, one fifth of the dust content in the raw syngas from the fluidized coal gasifier), while the raw syngas from the fluidized coal gasifier has high steam content (water-gas ratio is up to 37%, volume concentration, the same hereinafter), so the dust removal method using baghouse filter in the prior art cannot effectively remove dusts from the syngas produced by the fluidized coal gasifier. Due to the condensation of steam and high dust content in the raw syngas from the fluidized bed, the baghouse filter will be blocked during the dust removal process so as to reduce the dust removal efficiency.
In addition, dust recycle after the dust removal is another common technical problem for the raw syngas from the fluidized bed coal gasifier in the prior art. An embedded scraper mechanical transport method is commonly used to recycle the dusts, but this technology works under normal pressure while the dusts are removed from the raw syngas produced by the fluidized bed gasifier under certain pressure. Therefore, the embedded scraper mechanical transport method is not applicable in this case. It is also difficult to use the water spraying dust removal method to solve the above problem because the coal ashes collected from the raw syngas produced by the fluidized bed gasifier have high carbon content and hydrophobicity.
Currently, pneumatic conveying apparatus is also widely used in the transportation of dry powder (such as flour, sugar powder). However, the fine coal ashes (10 microns) collected from the raw syngas produced by the fluidized bed gasifier after the dust removal have high steam content and tend to be mushy, so those skilled in the art usually consider the pneumatic conveying apparatus not applicable to deliver the coal ashes collected from the raw syngas produced by the fluidized bed gasifier after the dust removal.
Further, star-shaped feeding valve is requisite in the dilute phase pneumatic conveying apparatus. This kind of star-shaped feeding valve cannot endure high pressure, which will easily result in gas leakage or ash ejection.